1. Field of the Invention
The invention relates in general to key structures and in particular to key structures switching between a normal state and a depressed state.
2. Description of the Related Art
Referring to FIGS. 1A and 1B, a conventional key structure primarily comprises a substrate B, a first rod L1, a second rod L2, a key cover C, and an elastic dome E disposed between the substrate B and the key cover C. The first rod L1 has a first end L11 and a second end L12, and the second rod L2 has a third end L23 and a fourth end L24. The first and second rods L1 and L2 are pivotally connected via a hinge H. As shown in FIGS. 1A and 1B, the first and fourth ends L11 end L24 are pivotally connected to the substrate B and key cover C. The second and third ends L12 and L23 are movable along axis X and pivotally connected to the substrate B and the key cover C.
When the key structure is depressed by an external force, from the state shown in FIG. 1A to the state shown in FIG. 1B, the key cover C descends from the height h1 to the height h2, and the elastic dome E is compressed. When the external force is released, the elastic dome E exerts a recovery force on the key cover C, such that the key cover C returns to the height h1. It can be difficult to depress the key cover C because the elastic dome E inevitably exerts an upward recovery force perpendicular to the substrate B against the external force.